This invention relates generally to a machine for wrapping a film sheet about a package by means of pivoting side folding levers and a coordinated rear folder and, more particularly, to an improved method and apparatus for folding film in such a wrapping machine.
A popular design of film wrapping machine provides for the wrapping of packages, particularly articles supported on trays, by elevating the packages into stretched film sheets. The length and width of each film sheet is selected to correspond to the package to be wrapped and the sheet is stretched above an elevator supporting the package. The package is elevated into the stretched film sheet and three sides of the sheet are folded under the package by means of side folding levers or underfolders and a coordinated rear folder or underfolder. The fourth side of the film sheet is folded under the package as the package is ejected onto an exit conveyor. Such a wrapping machine is fully described in U.S. Pat. No. 4,510,731, entitled "Film Wrapping Machine Including Film Length Selection," which is assigned to the same assignee as the present application and is incorporated herein by reference.
The film wrapping machine disclosed in the referenced patent can wrap a wide range of package sizes having base dimensions which vary from approximately 5 inches by 5 inches to approximately 9 inches by 12 inches in two different width films. While a large variety of film widths are available, two standard width films used by the machine are 14 inches and 18 inches. In many applications, as many as twenty differing package sizes are wrapped by the machine by selecting an appropriate width and length of film to be wrapped about each of the packages. However, the maximum size package which can be wrapped by the machine is limited by the width of the package handling path through the machine and/or the width and length of film which can be drawn into the machine to wrap a package.
Oversized packages which have dimensions exceeding 9 inches by 12 inches and often referred to herein as family sized packages or "family packs," can be wrapped by the machine in the larger standard width film used by the machine. Unfortunately, the edges of the underfolded sides of a sheet of such film used to wrap a family pack by the machine are not completely overlapped with one another. Without complete overlapping of the edges of the underfolded sides of the film sheet, unacceptable gaps are formed in the wrappings on the undersides of the packages. While film adheres well to itself and the adhesion can be strengthened by the application of heat, film does not adhere well to typical packages or trays used to support articles to be wrapped. Unless an overlapping seal is formed, the wrap about a package would be loose and unacceptable, particularly for food products.
To overcome the problem and be able to wrap family packs, the existing wrapping machine has been modified to expand the package handling path and permit wider 21 inch film to be used by the machine. However, such changes are expensive and require the modification or replacement of a large portion of the wrapping machine. Further, the wider film is a continuing increased expense in operating the machine.
Alternately, adjustments to the film pulling apparatus or replacement of the film pulling apparatus to provide extended film draw are possible. With extended film draw, family packs can be accommodated by feeding such packages into the machine lengthwise rather than in the standard widthwise manner. While such an approach may be economically more attractive than widening the existing wrapping machine, it still requires the modification or replacement of a substantial portion of the machine or repeated adjustments to the machine such that both the standard range of package sizes and the larger family sized packages can be wrapped.
It is, thus, apparent that the need exists for an improvement to existing film wrapping machines such that family sized packages can be wrapped in a standard width film used by the machines. To be practical, the improvement cannot require extensive changes to the wrapping machines and must permit the machines to wrap packages within the standard wide range of package sizes which normally comprise the majority of the packages wrapped.